Network eor neutralizing- the stjsceptaijce of a loaded line



Dec. 4 1923.

R. S. HOY'T NETWORK FOR NEUTRALIZING THE SUSCEJPTANCE OF A LOADED LINE 2 Sheets-Sheet Filed July 9. 1919 A TTORNEY Dec. 4, 1923. 1

- R. s. HOYT NETWORK FOR NEUTRALIZING THE SUSCEPTANCE OF A LOADED LINE Filed July 9, 1919 2 Sheets-Sheet 2 7 ATTORNEY IN V EN TOR.

Patente-d Dec. 4, 1923.

RAY S. HOYT, OF BROOKLYN, NEW YORK,

PATENT OFFICE.

ASSIGNOB TO AMERICAN TELEPHONE AND TELEGRAPH COIMPANY, A CORPORATION OF NEW YORK.

NETWORK FOR NEUTRALIZING- Application filed July 9,

To all whom it may concern: 7

Be it known that I, RAY S. Hor'r, residing at Brooklyn, in the county of Kings and State of New York, have invented certain Improvements in Networks for Neutralizing the Susceptance of a Loaded Line, of which the following is a specification.

My invention relates to a circuit arrangement associated with a periodically loaded transmission line, which arrangement is hereinafter termed, in accordance with common usage, a network. The object of the invention is; to provide a network having a purely susceptive admittance substantially equal and opposite to the susceptance component of the characteristic admittance of a periodically loaded line over a wide range of frequencies, such for instance as the range of frequencies necessary for the telephonic transmission of speech. A further object of my invention is, by the co-operative combination of said network and said loaded line, to provide a transmission system whose admittance is substantially that of a constant conductance over said range of frequencies; so that the impedance of such transmission system shall be substantially that of a constant resistance over said range of frequencies.

It is a well-known fact that the non-- loaded transmission line has a characteristic impedance which is substantially that of a pure resistance over the range of telephonic frequencies; It is further known that the characteristic impedance of the ordinary periodically loaded line varies greatly over the range of telephonic frequencies; besides depending greatly on the fractional length of the initial section or on the fractional value. of the initial coil. as the case may be. The impedance characteristics of the nonloaded line and the periodically loaded line are. therefore, quite dissimilar.

In telephony it is often desirable and necessary to connect a periodically loaded line in series with a non-loaded line. 0 'ing to the above mention-ed dissimilar impedance characteristics of said lines, a reflection of telephonic waves, with consequent energy loss and inferior transmission, results when the said lines are connected directly in series for the telephonic transmission of speech. My invention contemplates providing and prefixing to the loaded line. a network and choosing a particular fractional value for SUSCEPTENGE OF A LOADED LINE.

1919. Serial No. 309,634.

the initial load coil the loaded line Whereby the impedance of the combination is substantially that of a pure resistance over a pro-assigned range of frequencies, for example, the range of frequencies necessary for the eliicient transmission of speech signals. lVhen this combination is connected in series with a non-loaded line, prefer ably through an autotransformer, the impedance characteristic of the arrangement, as seen from the sending end of either the non-loaded line or of the loaded line, is substantially that of a single continuous trans mission line.

The network of my present invention, though possessing properties closely analogous to those of the network disclosed in my previous Patent No. 1,23,0(36, dated October 16, 1917, is nevertheless entirely distinct therefrom and independent thereof. Not only is it entirely different in form, but it is also different in function, in that it neutralizes the susceptance of the loaded line at a point in a loading coil instead of neutralizing the reactanee at a point in a loading section. The analogy between the network of my present invention and the network of my aforesaid previous invention consists in the fact that the mathematical expression for the susceptance of my present network is of the same form (when regarded as a function of the frequency) as the mathematical expression for the reactance of my aforesaid previous network; while, with reference to the loaded lines themselves, there is a similar correspondence between the mathematical expressions for the susceptance and the reactance neutralized by the respec tive networks. Stated more specifically, my

present network neutralizes the susceptance of a loaded line that terminates with a certain fractional loading-coil, with the same precision as my aforesaid previous network neutralizes the reactance of a loaded line that terminates with the corresponding fractional loading section. In consequence of this analogy between the two types of networks, it follows that for every possible application of either type there exists a corresponding possible application of the other type. On the whole the two networks possess about equal utility except for the fact that the network of my present invention is of shunt type and therefore does not require subdivision in order to maintain the bilatertill al symmetry of the transmission line, while the network of my aforesaid invention is Oil series type and therefore usually requires ac-- curate. subdivision in order to maintain the symmetry (as indicated by Figs. 2, 3, and 5 of the aforesaid Patent No. 1,2 l3,066); in practice, this difference would usually constitute a very substantial advantage in favor of the shunt type.

My invention is best understood by reference to the accompanying drawings in. which Fig. l is a diagram illustrating the network; Fig. 2 is a diagram illustrating the network connected to a periodically loaded line; Fig. 3 is a diagram illustrating a non-loaded line connected through an autotransformer and the network of invention to a periodically loaded line; Fig. 4 is set of curves illustrating the conductance component of the characteristic admittance or he periodically loaded line as a function of the frequency; Fig. 5 is a diagram illustrating a loaded line connected between two non-loaded lines, with a network at each of the two junctions, and Figs. 6, 7 and 8 are diagrams of the arrangements of my invention embodied in a l-wire transmission system comprising two side circuits and a phantom circuit.

The general theory underlying this invention will now be presented. Such theory can 'be based more simply and more conveniently on a general formula for the, char acteristic m-load admittance of a periodically loaded line than on the corresponding formula for its reciprocal, the characteristic load impedance. For any fixed frequency and initial termination, said admittance, as is well known, depends mainly on the line capacity and on the load coil inductance; but also, to a slight extent, on the distributed line inductance. This small effect produced by the distributed line inductance will not be neglected, but will be taken into account in the same manner as has already been described in my copending application No. 309,633 filed of even date herewith, and

vmore fully set forthin my previous Patent Flo. 11,167,693; wheein it is shown regards characteristic mid-load impedance {and hence as regards characteristic midlOllll admittance), aodica ly loaded line having ('listributed line inductance in addition to its lumped load inductance is simulated to a high degree of precision by a certainperiodically loaded line having no distributed lin inductance but having an inductai ce L, per load coil and a capacity 5C per loading section; where s is the spac ing of the load coils, that is, the distance between adjacent coils, and L, and C, are approximately equal. to the corresponding cmistauts of the actual loaded line, that is, to its inductance L per load coil and to its capacity C per unit length, respectively, said names"? V and (16) of my aforesaid 1,167,693

where i denotes the imaginary operator 1 and T and W have the same significance as 111 my aforesaid copending application in which 2) is 9m times the frequency in cycles per unit time.

ll riting l) and Q, for the conductance and susceptance components of the characteristic aldmittance Z so that ZzD-l-ZQ, it follows tiat Expressing VV in terms of p, as given by equation (3), and also substituting the value of T, as given by equation (2), the above expression for Q, reduces to Now consider the susceptance of a ca pacity element in series with an inductance element L The susceptance of this an rangement is well known to be enpressable as:

l 93(1 .r)sl li p equations (6) and (7) form as Comparison or news that thgards the in, may be made proportioning C (523 1/73) all,

Of course physical. limitations restrict the choice of to thos values for which Q, and. v are positive; but that means only hat a: ltnnot be less than 1 and cannot el-zcced l, whileit can have any value between those llil two extremes. Thus if the value of :0, which is the ratio of the inductance of the initial.

coil to the inductance of each of the following coils, lies between 9; and 1 the combination of a capacity element 3 and an inductance element L in series, the values of said elements being proportioned in accordance with equations (8) and (9), has a susceptance equal and opposite to the characteristic susceptance of the periodically loaded line characterized by the parameters 860 and L.

If now the admittance element having susceptance Q, is prefixed in shunt to the periodically loaded line of characteristic admittance Z the admittance of the combination is obviously Z{z'Q.,. If, further, the component elements of Q, are proportioned in accordance with equations (8) and (9), then Q,,:Q, so that the admittance of the combination reduces to D as given by equation Thus it is seen that the admittance of the combina tion has no susceptance component. D, as given by equation (4k), is a function of m, and, therefore, of the frequency, since 2.0,, is directly proportional to the frequency. The value of D/T is proportional to the conductance component, since T is a constant for any particular line. By reference to equation (a and if from this equation we calculate the values of D/T for different values of w from O to 1. and plot these values of D/T against the corresponding values of w, we get the middle curve shown in Fig. 4 of the drawings. It will be noticed by reference to said Fig. at that the value of D/T is approximately constant and closely equal to unity from 20 :0 to to -:09. The corresponding range of values of frequency is substantially the range usually necessary for the telephonic transmission of speech. it should be noticed, however, that this constant conductance component characteristic conditioned by the choice of a particular ralue of 00, namely about 0.8, and that for values of differing materially from 0.8 this desired characteristic does not hold. actual loaded line does not, of course, begin in general with an 0.8 coil, the actual termination of the line being governed generally by geographic factors and certain considerations of convenience entirely foreign to the present invention, but it can always be built out artificially to an 0.8 initial coil or to any other initial termination, as fully explained To summarize the foregoing, the combination of a networ: proportioned in accordance with equations (12) and (13), and illustrated in Fig. 1, prefixed in shunt to a periodically loaded line whose initial coil has an inductance equal to approximately 0.8 of the inductance of each of the following coils, has an admittance whose susceptance component is substantially zero and whose conductance component is substantially constant and equal to T over approximately the entire frequency range below the critical frequency (the critical frequency being that frequency for which w is equal to unity); and has, therefore, an impedance whose reactance component is substantially zero and whose resistance component is substantially constant over that frequency range. The value of T is given by equation (2) above.

I do not desire to limit the proportioning of the network of my invention rigidly to formulas and (9) or to values of :v exactly equal to 0.8. If very high precision is not necessary, I may, for instance, with small loss in precision, proportion 0 and L,

in accordance with the following formulas which are obtained by neglecting the dis tributed inductance of the loaded line.

O. ,:3$C/10 (let) L :8L/15 (15) On the other hand, if extremely high pre cision is desired, I may choose for a: a value slightly different from 0.8; or I may com-.

2' those given by equations (8) and (9) of this sp cification, with :1: equal to about 0.8. The

actual numerical values of C, and L depend on the values of 3G,, and L that is, on the constants of the particular loaded line with which it is desired to associate said network,

and also on the particular value chosen for :12.

Referring to Fig. 2, 1 is a periodically loaded line having load-coils 2, 2 2", etc., inserted at regular intervals along the line. The inductance of the initial load coil 2 is approximately 0.8 of the inductance of each of the following coils 2, 2 etc. It the ac 'tual line does not have an initial 0.8 coil, it may be artificially built out o an ccpi'ivalent mentioned 0.8 initial coil as hereinbel ore mentioned and fully explained in my above patents and copending application. i refined in shunt to terminals o, is adni ttancc l comprising a capacity element 5 in series with an inductance element the line 1 is characterized by the parameters RC and L and 00, the capacity element is so proportioned that its capacity equal to (T and the inductance element 6 is so proportioned that its inductance equal to li,, where Q and L, are given by equations (8) and (9), with a: equal to about 0.8. l rom the theory developed in this specification it follows that the admittance ot the comb:na tion as seen from terminal 7, T will be sub stantially that of a cons ant conductance equal in value to LEGO/L0; and hence its impedance will be tially that of a constant resistance value equal to Referring to Fig. 3, the arrangement of 2 is connected through an autotransformer 8 to a i'initorni non-loaded line 9. will be understood that an equivalent transformer may replace the autotransitorincn cept when conductive connection is desired. 'lcrininals 7, 7 of the loaded line system are connected to terminals 10, 10 of autotra former 8, while line 9 is connected to terminals 11, 11 of said autotransformer. lit the nonloaded line has a distributed inductance J per unit length and a distrilnited capacity C per unit length, its characteristic in; pedance is well known to be approximately equal, except at very low frequencies, to

the impedance of the entire system as seen ri t-racer from any point in tee non-loaded line will be versely, when the non-loaded line is etlectively infinitely long, the impedance of the entire system as seen from any point in the loaded line is the same as the impedance of an infinitely long loaded line. As hereinhetore stated this is the condition for propaion without reflection losses.

r igs. 2 and 3 have been given for the purpose of illustr ting the use of a single neutralizing network; Fig. 2 showing); such a network prefixed in shunt to a periodically loaded line. and ll' ig. 3 shov-ring the so modified periodically loaded line connected to a non-loaded line (through a suitable transformer). l ig. 5 is given to illustrate the simultaneous use of two such networks 4i, 1- one at each end of piece of loaded cable 1 occurring between two non-loaded lines 9, 9. n case either or the nondoaded lines difrs in impedance from the loaded line, it is to be understood that a transformer of suit able ratio would be inserted at the corresponding junction, as in Fig. 3). In consequence of the networks 4, 4 the impedance oi the system as seen from any point in either non-loaded line is substantially the same as the impedance of an infinitely long; non-loaded line; while, as seen from any point in the loaded line, the impedance of the system in each direction is substantially the same as the impedance of an infinitely longloaded line.

In loaded line systems it is customary and desirable to employ two parallel and prel? erahly similar circuits as the two sides of a third circuit called the phantom circuit. l'l' neutralizing networks of 1y invention are to be employed in such a system to neutralize the susceptance of the two side circuits and of the phantom circuit, means must be provided whereby the neutralizing arrangement associated with any one circuit shall not ailect the transmission of current in the other circuits. Fig. 6 is a dia grain of a susceptance neutralizing arrangent designed to be prefixed to such a sysm and to satisfy the requirement just mentioned. Referring to 6, conductors 22 and 23 constitute one side circuit 2%, and in parallel they serve as one side of the phantom circuit; similarly, conductors 22 and 23 constitute the second side circuit 24, and in parallel they serve as the other side of the phantom circuit. The two side circuits and the phantom circuit are represented as being periodically loaded and as terminating with fractional load coils connected to terminals 20, 21, 21 of the neutralizing arrangement. Considering the side circuit 2a, the network of my invention associated therewith is represented by an arrangement comprising a condenser 26 having a capacity equal to C and an inductance coil 27 having an inductance equal to L U and L being computed from the constants of line 2+1- as hrreinbciore explained. It will be evident, thereipre, that the network 25 oilers to the voltage inipressed on line 2% an admittance equal to that of the network N of Fig. 1. provided. of course, that C and L are proportioned in accordance with the constants of line 24. It will be further evident that network 2 produces no eitect on the phantom current flowing in conductors 22 and 23. since said two conductors are then at the same potential.

Network 25 is similar in its component parts to network 25 and is the neutralizing network of line The condenser 26 and the inductance coil 27 are. of course, proportioned in accordance with the constants of line 24. In ordinary practice, lines 9% and 2a would be alike. in which case networks 25 and 25 would be alike.

The circuit arrangement 28 comprising a condenser 29 and an inductance coil 30, together with the tour auxiliary inductance coils 31, 31, 31, 31. constitutes the neutralizing network of the phantom circuit. The two auxiliary coils 31, 31 are wound on a common magnetic circuit and are so related thereto that said coils 31, 31 are non-inductive with respect to the phantom circuit cur rent in line 2 while at the same time they can be made off sntliciently high impedance to produce but a negligible effect (except at very low frequencies) on the side circuit current in line 24. The auxiliary coils 31. 31', are similarly related to line 24 and to tl e phantom circuit. The capacity of the element 29 is made equal to C and the inductance of the element IE0 is made equal to L where C and L, are computed from the phantom circuit constants in the manner hereinbefore explained. It will be evident then, that as regards the phantom circuit, the circuit arrangement 28 is equivalent to the network of Fig. 1, and that further its insertion in the circuit will not appreciably affect the transmission of the side circuit currents.

It will be understood that it is not always necessary to employ the entire neutralizingarrangement of Fig. 6: for example. it the phantom circuit non-loaded while the side circuits are loaded, the network 28 is omitted together with the auxiliary coils 31. 31.31,

31. It should be further observed that, while I have shown the network of my invention as proportioned in accordance with an actual loaded line. it may likewise be proportioned to neutralize-the susceptance of an artificial loaded line. A well known form oi. artificial loaded line consists of a number ot coils of substantially equal impedance connected in series with the line and a number of condensers of substantially equal capacity connected in shunt thereto, alternately with the said coils. The coils correspond to the loading coils of the geographical loaded line and the condensers correspond to the distributed capacity per section between loads of the geographical loaded line. The term loaded line as used throughout this specification designates both the geographical and the artificial form of line, unless the context restricts the meaning otherwise.

The arrangement shown in Fig. 7 accomplishes the susceptance neutralization for the two side circuits and for the phantom circuit without the employment of the auxiliary coils 31, 31 and 31, 31. In this a rrangcment the side circuit neutralizers are constructed symmetrically so as to afford a pair of neutral midpoints m, m to which the phantom circuit neutralizer is connected. Strictly, the neutralizer connected to these neutral points accomplishes only a part of the neutralization for the phantom circuit, the remainder of such neutralization being accomplished by the side circuit neutralizers in consequence of their effective connection with the phantom circuit through the neutral points m, m. Thus, while the proportioningof the side circuit nentralizers depends only on the constants ol the side circuits, and is, therefore. independent ot the presence or absence of a phantom circuit neutralizer. the proportioning oi the phantom circuit neutralizer depends not only on the phantom circuit constants, but also on the side circuit constants. Consequently in practice the side circuit neutralizers are first pmportioned in accordance with the formula (8) and (9) already given, due allowance being made for the necessary subdivision of each condenser element into two serially connected parts to meet the requirements for symmetry. Next the. phantom circuit neutralizer is proportioned by means of the same design formulae by substituting therein the constants of the phantom circuit and then correcting for the effective capacity and the effective inductance contributed to the phantom circuit neutralizer by the two side circuit neutrallzers.

In certain cases it is more convenient to determine, first, the susceptance required to neutralize the phantom circuit and connect the same into the system as shown in Fig. 8. If it is then found that the side circuits require additional susceptance for their complete neutralization, the same may be introduced therein by additional networks, 35 and 35 shunted across the side circuits,

n Oi

The uses "of my invention are not limited to the cooperative arrangements illustrated herewith, but my invention is applicable to any arrangement wherein it is de rblc that a periodically loaded line 'L, substantially no susccptive admittance d hence no eactive impedance. As examples ot further uses, my invention may be employed: to connect. a loaded line type or filter to repeater element whose impedance is nearly constant resistance; (2} to connect a loaded line to repeater system whose impedance is nearly constant resistance; to connect a loaded line to terminal apparatus whose impedance is nearly constant resistance.

Finally, I desire to emphasize the tact that to secure for the loaded line equally good impedance properties without employi either the network oi my present invention or the network of my previous invention (Fig. 1, latcnt No. 1,243,066) would necessitate spacing the loading coils at much closer intervals. For it the UOlTWOl'l-(S were omitted the critical l'reque; 1y the loaded line would have to be very much increased to maintain substantially the pie-existing impedance properties over the contemplated frequency-range; and, with the impedance approximately fixed, an increase in the critical frequency can be attained only by a correspondingly closer spacing of the loading coils.

Although only a few forms and arrangements of apparatus embodyingthe invention are shown and described herein, it is readily understood that various changes and modifications may be made therein within the spirit and scope of the following claims without departing from the scope of tle invention.

hat is claimed is:

1. A net-work for neutralizing the characteristic susceptance of a periodically loadee signaling line beginning at a point in a loading coil, said network comprising precomputed admittance elements so proportioned in a-cordance with the constants of said line that the susceptance of said notwork is substantially equal and opposite to the characteristic susceptance or said line beginning at a point in a loading coil.

2. A network for neutralizing the characteristic susceptance o1. periodically loaded signalingline beginning at a point in a loading coil, said network comprising inductance and capacity elements so proportioned in accordance with the constants of said line that the susceptance of said network is substantially equal and opposite to the characteristic susceptance of said line beginning at a point in a loading coil. V

3. A network having a susceptance equal and opposite to that of an actualv loaded sip;- naling transmission line beginning at a point in a loading coil, said network comprising sha ll lit ravens? inductance and capacity elements having precomuted values dependent on the loading coil inductance, the distance between consecutive loading coils, and the distributed capacity and inductance of said line.

l. A network having a susceptance substantially equal and opposite to the characteristic susceptance of a periodically load-- ed signaling line, said network comprising an inductance coil in series with a condenser. the values of the inductance of said coil and the capacity of said condenser being precomputed in accordance with the loading coil inductance, the distance between consecutive loading coils and the distributed pacity and inductance of said loaded i.--

5. In a signaling system, the combination of a periodically loaded transmission line and a network connected in shunt therewitln said network consisting of inductance and capacity elements so proportioned in accordance with the constants of said loaded line that the admittance of said combina tion is a practically pure, constant conductance over a pro-assigned range of frequen cies.

6. In a signaling system, the combination or two parallel transmission lines constituting); two side circuits and. a phantom circuit, said circuits being periodically loaded, and a plurality of networks connected in shunt therewith, said networks including; admittance elements so proportioned that the subceptance of each of said circuits is substantially neutralized.

7. In a signaling system, the combination of two parallel transmission lines constituting; two side circuits and a phantom circuit, said lines being periodically loaded as regards each side circuit and also as regards said phantom circuit, with two similar and equal networks one in shunt with each of said side circuits and a connection between said networks for associating the same with the phantom circuit, each oft said networks including precomputed inductance coils and condensers so proportioned in accordance with the constants of said side circuits and said phantom circuit that the impedance of the combination, as seen from each of said side circuits, and from said phantom circuit, is approximately a pure noninductive re sistance over a pro-assigned range of frequencies.

8. In a signalling system, tour parallel conductors constituting two separate transmission lines, and providing two side circuits and one phantom circuit, said. conductors being periodically loaded as regards each side circuit, and also as regards the phantom circuit, each of said circuits including impedance elements connected in shunt thereto, said impedance elements being so related that the characteristic impedance of each side circuit and of the phantom circuit is substantially a pure constant resistance over a pre-assigned range of frequencies.

9. The combination or" a loaded line comprising lump series inductanccs and shunt capacities, with a ne work comprising an inductance coil in series with a condenser, said network being connected in shunt to said line and having a susccptance substantially equal and opposite to that of said loaded line beginning at a point in a loading coil, and the values of the inductance of said inductance coil and the capacity of said condenser being proportioned in accordance with the inductance and capacity of said loaded line.

10. A device for neutralizing the susceptance of a phantomed periodically loaded line, comprising a network for neutralizing the susceptance of each side circuit, and arranged to provide a point neutral to each side circuit, and a network for neutralizing the susceptance of the phantom circuit connected between said neutral pOintS.

11. In a device "for neutralizing the susceptance of a loaded transmission line, having side circuits and phantom circuits, a pair of networks connected in series with each other across each side circuit, a common connection uniting the pairs at their middle points, said networks being of a value to fully neutralize the line as to one of the two kinds of circuits, and a network located exclusively in the other kind of circuit to neutralize the remaining susceptance of the circuit without affecting the first named neutralizing devices.

12. In a signaling system, the combination of a non-loaded line comprising two sections, with a loaded line interposed between said sections, and a plurality of networks shunted across the terminals of said loaded line to neutralize the susceptance thereof over a pre-assigned range of frequencies.

13. In combination, a circuit comprising shunt capacity and lumped series inductanccs placed at substantially equal capacity intervals, and a network for changing the impedance of said circuit to a substantially constant resistance over a wide range of frequencies, said network comprising inductive and capacity reactance elements connected in series with each other and in shunt to the said circuit, said elements having their magnitudes determined to make the impedance of the entire combination substantially a constant resistance over a wide range of frequencies. 4

14. A circuit comprising shunt capacity and lumped series inductances placed at substantially equal capacity intervals and an impedance device connected in shunt to said circuit, said device having a reactance substantially equal and opposite to that of the remaining part of the circuit throughout a wide range of frequencies.

17 In a combination, a plurality of transmission lines associated with each other in tandem, said lines having different ratios of reactance to impedance, and means shunted across said lines at their junction, for substantially equalizing said ratios.

16. In COI11blI1LtiO11,-L conductor pair comprising equal inductances in series, equal shunt capacities alternating therewith, said conductor pair having at its initial end a series inductance substantially 0.8 of the other inductances, and a shunt across the initial end comprising inductance and capacity in series.

17. In combination, a loaded line and at 0.8 load therein an inductance and capacity in series with each other and across the line and of proper value to reduce the impedance of the line substantially to a pureresistance.

In testimony whereof, I have signed my name to this specification this 8th day of Jul 1919.

RAY S. HOYT. 

